请求被中止: 未能创建 SSL/TLS 安全通道。

使用HttpWebRequest请求https接口时抛出异常：请求被中止: 未能创建 SSL/TLS 安全通道。

代码如下：

   public string PostDataToHttpsUrl(byte[] data, string url)
        {


            #region 创建httpWebRequest对象

            HttpWebRequest httpRequest = WebRequest.Create(url) as HttpWebRequest;

            httpRequest.ProtocolVersion = HttpVersion.Version10;
            ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;

            if (httpRequest == null)
            {

                throw new ApplicationException(

                    string.Format("Invalid url string: {0}", url)

                    );

            }

            #endregion



            #region 填充httpWebRequest的基本信息

            httpRequest.UserAgent = sUserAgent;

            httpRequest.ContentType = sContentType;

            httpRequest.Method = "POST";
            httpRequest.Proxy = null;

            #endregion



            #region 填充要post的内容

            httpRequest.ContentLength = data.Length;

            Stream requestStream = httpRequest.GetRequestStream();

            requestStream.Write(data, 0, data.Length);

            requestStream.Close();

            #endregion



            #region 发送post请求到服务器并读取服务器返回信息

            Stream responseStream;

            try
            {

                responseStream = httpRequest.GetResponse().GetResponseStream();

            }

            catch (Exception e)
            {

                // log error

                //Console.WriteLine(

                //    string.Format("POST操作发生异常：{0}", e.Message)

                //    );
                //Console.ReadLine();
                throw e;

            }

            #endregion



            #region 读取服务器返回信息

            string stringResponse = string.Empty;

            using (StreamReader responseReader =

                new StreamReader(responseStream, Encoding.GetEncoding(sResponseEncoding)))
            {

                stringResponse = responseReader.ReadToEnd();

            }

            responseStream.Close();
            return stringResponse;
            #endregion

        }